1. Technical Field of the Invention
The present invention relates in general to the field of communication systems, and in particular, by way of example only, to prevention of signaling traffic overload within a cellular communication system employing a location management scheme.
2. Description of Related Art
Modern cellular communication systems, such as cellular communication systems based on IS-136 specifications, typically employ a location management scheme that enables the cellular network to quickly locate a target mobile station in response to an incoming call. In a zone-based location management scheme, for example, the cellular coverage area is divided into non-overlapping location areas, where each location area may include one or more individual cells. When a mobile station powers up or enters a new location area, the mobile station initiates a location update request or registration over a reverse access channel associated with the serving base station. The cellular network then accesses the Home Location Register associated with the mobile station and updates the stored indication of the mobile station's current location. When the cellular network receives an incoming call addressed to a target mobile station, the cellular network usually broadcasts a paging message over forward control channels associated with all the base stations within the target mobile station's last updated location area. The target mobile station responds by transmitting an acknowledgment message over the serving base station's reverse access channel, thereby enabling the cellular network to identify the base station currently serving the target mobile station and to route the incoming call accordingly.
The forward control channel(s) of cellular networks are conventionally used for other messages besides paging messages. In other words, the forward control channel(s) are typically shared among many different types of messages that are transmitted from the cellular network to one or more mobile stations. For example, access response messages may share the forward control channel(s) with paging messages. An access response message is a message sent from the cellular network to a specific mobile station that has previously requested access to the cellular network (e.g., a specific mobile station that has requested initiation of a phone call).
In order to complete an incoming call in a timely fashion, among other reasons, paging messages are frequently given priority over access response messages. Unfortunately, one resulting significant problem associated with cellular communication systems is that paging messages may supplant access response messages. One particularly onerous result of this situation is that the forward control channel may become so congested with paging messages that access response messages cannot be transmitted. Consequently, a base station's forward control channel can become completely consumed with the sending of paging messages to mobile stations that are not even within the cell associated with the base station (e.g., because the paged mobile stations are within cells associated with other base stations that belong to the same location area). Meanwhile, mobile stations within the base station's cell that are attempting to establish a call, and hence actively receiving and detecting messages in an attempt to detect an access response message, may be unable to do so.
Base station resources that are still available (e.g., traffic channels) may therefore go unused. Because congestion of forward control channel(s) results in lost calls from unsuccessful call setups, the efficient management of the forward control channel(s) is critical for providing reliable mobile service to mobile stations traveling within the serving coverage area.
An existing approach used in the Personal Digital Cellular Standard (PDC) of Japan (RCR STD-27F) (formerly called the Japanese Digital Cellular System (JDC)) relies on reserved capacity for access response messages and paging messages. In PDC systems, paging messages can consequently never occupy the total capacity. Under the TIA/EIA-136 standard, on the other hand, paging messages can occupy the total capacity. Using a fixed (or slow) assignment of resources, as is done in PDC, is a less than optimal manner for handling traffic capacity. For example, paging messages may become backed up, which causes incoming calls to be lost, while excess capacity reserved for access response messages goes unused. Permitting the entire capacity to be used for paging, as is done in TIA/EIA-136, can cause a mobile that has already contacted the network and is waiting for a response to never receive one. For example, if the entire forward control channel capacity is occupied with higher priority paging messages, then no lower priority access response messages will be transmitted.